Natural Does Not Mean Inert: Desiccant Dusts, the Silica Gel Advantage and What the Double-Blind Trials Found

1. Introduction: the appeal and the problem

Desiccant dusts are the most intellectually satisfying tool in pest management. They work by a purely physical mechanism, they do not degrade the way an organic molecule does, and an insect cannot evolve an enzyme to detoxify a lack of water.

They are also sold to the public on a framing that this paper argues is misleading in two directions: that natural means safe, and that diatomaceous earth is representative of the category.

1.1 Why this matters commercially

Diatomaceous earth is the product a householder buys, because it is available in hardware stores and garden centres and is marketed as a natural alternative. Silica gel is the product a professional buys. The evidence reviewed here indicates that gap is not a marketing artefact.

2. The mechanism

The mode of action of inert dusts against insects was described as early as 1930, when researchers stated that the mode of action was mainly due to desiccation.³

2.1 The common misconception

Inert dusts kill insects by desiccation. They desiccate not by absorbing water, but by removing, through abrasion or absorption, the outer layer of wax or grease that is part of an insect's exoskeleton.⁴

This distinction is frequently lost in consumer material, which describes the dust as drying the insect out directly. It does not. It removes the barrier that prevents the insect drying itself out.

2.2 The waterproofing layer

The ultra-thin lipid layer of the epicuticle serves as a barrier against moisture loss.⁴ Removal of these lipids by mechanical, chemical or high temperature treatment significantly increases cuticle permeability.³

That final clause connects three otherwise separate interventions in this journal. Desiccant dusts remove the lipid mechanically, solvent-based formulations dissolve it chemically, and thermal treatment compromises it with heat. Three methods, one target.

2.3 The lethal threshold

Death occurs when the insect loses about 60 per cent of its water content.²

So it takes a certain time until insect mortality occurs, which determines these products as slow acting insecticides.²

2.4 The additional mechanisms

Toxicity arises primarily from physical attributes rather than chemical composition, and the mechanisms include absorption of cuticular waxes, cuticle abrasion, damage to the digestive tract, surface enlargement through dehydration, and obstruction of spiracles and tracheae.¹⁰

Cuticular damage may also increase vulnerability to entomopathogenic infection, potentially modulating host and pathogen interactions.¹⁰

3. Two different physical processes

The distinction between the two main products is mechanical and it explains the performance gap.

Diatomaceous earth is both abrasive and sorptive.¹ Like superfine sandpaper, it chafes and abrades the waxy outer coating of insect cuticle.⁴

Silica gel, in contrast, is non-abrasive.¹ Instead of acting as an abrasive, it functions somewhat like a sponge to absorb the cuticular waxes of insects onto the dust particles.⁴

3.1 What each material is

Diatomaceous earth consists of fossilised diatoms, microscopic single-celled algae whose hardened walls contain silica. Under magnification the fossilised remains look like hollow, perforated tubes, and the porosity and hardness make it useful industrially as a filtering agent.⁴ It is composed mainly of amorphous hydrated silica.¹⁰

Silica gels are synthetically produced compounds comprised of 99.5 per cent silicon dioxide. The forms used for pest control are light fluffy powders comprised of extremely small particles.⁴

3.2 The electrostatic property

One further difference matters for pickup. The tiny silica gel particles have an electrostatic charge that helps them adhere to insects crawling over treated surfaces.⁴

A particle that clings to the insect continues to act after the animal has left the deposit, which is the same carried-dose logic described for microencapsulation elsewhere in this journal.

4. What makes a dust effective

Efficacy is not a property of the label. It is a property of the material, and the parameters are published.

The toxicological efficacy of diatomaceous earth against insects greatly depends on amorphous silica content having uniform particle size below 10 micrometres, a high oil sorption capacity, a large active surface area, and very little clay and other metal oxides.³

4.1 Oil absorption as the key figure

There are a number of parameters of diatomaceous earth, including particle size, shape, active surface area, oil absorption, pH, density, age and species of diatoms, and chemical composition, that could affect insecticidal efficacy. Since the primary insecticidal action is absorption of lipids, the greater the oil absorption, the greater the efficacy. Commercial products range from 116 to 175 per cent oil absorption capacity.⁴

4.2 The ideal specification

Ideally, for pest management, the material should be a high purity amorphous silica of uniformly small particle size below 10 micrometres, containing very little clay and less than 1 per cent crystalline silica.⁴

Hold onto that last figure. Section 16 returns to it, and it is the difference between a reasonable product and a hazard.

4.3 Why this makes brand comparison difficult

A purchaser cannot read oil sorption capacity, particle size distribution or crystalline silica content off a retail package. Two products described identically as diatomaceous earth may differ across every parameter that determines whether they work.

5. The head to head comparison

The cleanest available comparison tested both forms against two bed bug strains of known resistance status.

Two desiccant dusts, a silica gel product and a diatomaceous earth product, were evaluated against two strains of Cimex lectularius, one highly pyrethroid-resistant and one insecticide-susceptible.¹

5.1 The result

Label-rate doses of both products produced 100 per cent mortality in both strains, albeit over dissimilar timeframes: three to four days with the silica gel against fourteen days with the diatomaceous earth.¹

5.2 Why the timeframe matters more than it appears

Both products reached complete mortality, which on a summary reading makes them equivalent. They are not.

Fourteen days is longer than the bed bug egg incubation period, which means a deposit killing over that interval is contending with continuous emergence. It is also longer than most occupants will tolerate a visible dust deposit, and §15 notes that deposits are nullified by accumulating household debris.

5.3 The tropical bed bug result

A separate evaluation against three pyrethroid-resistant Cimex hemipterus strains with documented cuticle variation, compared with a susceptible C. lectularius strain, found that desiccant dusts, particularly the silica gel, consistently achieved rapid and complete mortality in resistant strains, outperforming diatomaceous earth and pyrethroid-based dusts.⁹

In the same work, chemical dusts were more constrained: a deltamethrin dust was largely ineffective, while a combination product containing pyrethrin, piperonyl butoxide and silica gel killed the susceptible strain.⁹

6. The stored product finding

The same ranking appears in a completely different literature, which strengthens it considerably.

Against various stored product pests, diatomaceous earth has been found significantly less effective than non-abrasive silica gels, even when used in higher doses.¹

The use of amorphous silica gel effectively controls insects at significantly lower concentration in comparison with the concentrations of diatomaceous earth required.²

6.1 The abrasion paradox

This is worth pausing on. Diatomaceous earth has two mechanisms available to it, abrasion and sorption, while silica gel has only one. The material with fewer mechanisms performs better.

The implication is that sorption is doing nearly all the work and abrasion contributes little, which means the sandpaper analogy that dominates consumer explanation describes the less important half of the mechanism.

6.2 The grain handling constraint

Silica gel's advantage comes with a cost in that context: it significantly reduces bulk density and flowability of grain, which is why reducing the quantity of inert dust applied to grain is crucial and why researchers explore mixing diatomaceous earth with botanicals that have different modes of action.²

7. The laboratory numbers

Under controlled conditions diatomaceous earth performs well, and it is important to state this before §8.

Diatomaceous earth has been found effective, under laboratory conditions, at application rates between 1 and 8 grams per square metre, achieving 100 per cent mortality against adults over 9 to 15 days and 99 per cent mortality against nymphs after 2 days.¹

7.1 The dose response

A published dose series gives cumulative mortality by day across rates. At 8 grams per square metre, mortality reached 92.5 per cent on day one and 100 per cent by day four. At 4 grams per square metre it reached 96.5 per cent on day one and 100 per cent by day three. At 2 grams per square metre it began at 41.1 per cent and reached 100 per cent by day nine, and at 1 gram per square metre it began at 17.1 per cent and reached 100 per cent by day nine. All treatments on all days were statistically different from the controls.⁸

7.2 What the dose series shows

The rate strongly determines early mortality and matters less for the eventual endpoint. Every rate tested got there; the low rates simply took longer.

That is a favourable result for the product and it is the basis of most of the claims made for it. The next section is why those claims do not survive contact with occupied buildings.

8. The double-blind result

A study designed to remove investigator expectation produced markedly different figures.

In a double-blind evaluation of natural and green insecticides against bed bugs, a product containing 95 per cent diatomaceous earth with 0.25 per cent dinotefuran killed 27 per cent of bed bugs or less, depending on strain and substrate. A diatomaceous earth product and a botanical spray produced 11 per cent control or less. A silicate-based product showed no activity against bed bugs in the study.⁵

8.1 The comparison within the same study

The same study included a silica gel product described as 100 per cent amorphous silica gel applied at 2 ounces per 100 square feet.⁵

So the silica gel and the diatomaceous earth products were evaluated under identical blinded conditions, and the performance gap in §5 reappears.

8.2 The wider pattern

The existence of this result is acknowledged in the review literature. Two studies, one field trial-based and one double-blind laboratory study, have presented evidence that diatomaceous earth may be largely ineffective, against laboratory results showing it effective.¹

Both forms of desiccant dust possess discernible efficacy against bed bugs, although results have been variable depending on the product tested and the bed bug strains used.¹

9. Substrate and strain interact

The double-blind study reported a statistical finding that explains much of the variability.

Analysis showed a three-way interaction between treatment, substrate, and bed bug strain, with a highly significant result.⁵

9.1 What a three-way interaction means

It means the effect of a product depends jointly on what it was applied to and which population was exposed, and that no single number describes its performance.

A product achieving good control on one substrate against one strain may achieve poor control on another substrate against another, and the three variables cannot be separated.

9.2 The connection to the substrate article

This is the same finding reported in the preceding article in this journal for liquid residual applications, arriving independently for dusts. Substrate is not a background condition. It is a determinant of outcome interacting with everything else.

10. Tolerance in a resistant strain

The most unexpected result in this literature undermines a claim the category is usually sold on.

Sub-label rate exposure to the silica gel product indicated that the pyrethroid-resistant strain possessed a degree of tolerance to this product, surviving 50 per cent longer than the susceptible strain.¹

10.1 Why this makes mechanistic sense

The bed bug resistance architecture described elsewhere in this journal includes cuticular thickening as a layer that slows insecticide penetration. A thicker cuticle with more lipid is also a better barrier against evaporative loss.

So the same modification that resists a neurotoxin resists a desiccant, not because the insect evolved against dusts but because the defence is general.

10.2 The important qualification

This tolerance appeared at sub-label rate. At label rate both strains reached 100 per cent mortality.¹

The practical conclusion is therefore not that dusts fail against resistant populations. It is that under-application against a resistant population is more likely to fail than the same under-application against a susceptible one, which narrows the margin for error.

11. The humidity dependence

The environmental constraint on the whole category follows directly from the mechanism.

Some, but not all, insects that lose the protective wax layer under dry conditions succumb within hours from evaporative loss of body water through the remaining integument.⁶

Because some insects may replace surface wax quickly, a mild desiccant such as diatomaceous earth is not effective when the air is moist and has little evaporative power.⁶

11.1 The two-sided requirement

Dry air is needed for two reasons. It drives the evaporation that kills, and it prevents the insect restoring the lipid layer faster than the dust removes it.

In a humid environment the dust may still be removing wax while the animal replaces it, producing a stalemate that consumes the deposit and kills nothing.

11.2 The Manitoba angle

This is one of the few findings in this journal that favours local conditions. A Winnipeg interior in winter is very dry, because heated air at low outdoor temperature holds little moisture, which is close to the ideal operating environment for a desiccant dust.

Summer basements are the opposite case, and the same product in the same building may perform differently in January and July.

12. The cement layer

A structural detail explains why some species resist desiccants more than others.

Unaffected insects may have a protective basal cement layer in the cuticle that affords additional protection from desiccation.⁶

12.1 What this implies for species selection

Desiccant dust performance should therefore vary systematically by species according to cuticular construction rather than according to anything about the dust.

We have not found a comparative study ranking structural pest species by desiccant susceptibility on this basis, and it would be a useful one. The practical translation is that a product performing well against bed bugs should not be assumed to perform equally against cockroaches, ants or stored product beetles.

12.2 The knockdown expectation

These dusts affect most insects very slowly, usually over several hours, with symptomology of a gradual reduction in activity, slow loss of weight and eventual death. They do not provide rapid or sudden knockdown, and rapid knockdown or paralysis has not been observed even with heavy deposits.⁶

13. Why the field differs from the arena

One experiment isolates a variable that may explain much of the laboratory and field discrepancy, and the result is striking.

Bed bug activation by carbon dioxide appeared of minor importance in arena studies, but was crucial for eradication in student dormitories. All five bed bug-infested dormitories with a combined treatment of desiccant dust and carbon dioxide were freed of bed bugs, whereas eradication was not successful in any of the six dormitories with only desiccant dust treatment.⁶

The different results in the laboratory and field experiments were most likely caused by the longer activation and higher dose of carbon dioxide used in the field experiment.⁶

13.1 Why this is the key result for dusts

A desiccant dust is an entirely passive deposit. It can only act on an insect that walks through it, and the preceding article in this journal established that bed bugs shelter within a short distance of the host and move on host cues.

Carbon dioxide activates them. An activated population crosses deposits; a quiescent one sits in harbourage while the dust sits on the floor.

13.2 The general principle

This reframes the laboratory and field gap for the whole category. In an arena the insect has nowhere to go and must contact the treatment. In a room it has harbourage, and whether it contacts the deposit is a behavioural question rather than a chemical one.

That is a better explanation for the double-blind figures in §8 than any deficiency in the material itself, though we note it as reasoning rather than as a finding the authors made.

14. Not all products labelled the same are the same

A study comparing retail and professional sources found differences large enough to matter.

Researchers assessed bed bug mortality associated with several dusts, comparing silicon dioxide and diatomaceous earth from a pest management company against diatomaceous earth sold as a litter conditioner, diatomaceous earth from a supermarket, green clay, talc and sodium bicarbonate.¹¹

14.1 The result

One traditional cleaning earth demonstrated efficacy ranging from 75 to 100 per cent in permanent and short exposures, similar to the efficacy of diatomaceous earth from the pest management company. On the contrary, diatomaceous earth for litter conditioner, diatomaceous earth from a supermarket, green clay, talc, and sodium bicarbonate were found to be ineffective.¹¹

14.2 The implication

Supermarket diatomaceous earth was ineffective while professionally supplied diatomaceous earth was not. Both are diatomaceous earth.

Section 4 explains why: oil sorption capacity, particle size and purity vary between deposits and grades, and none of it appears on retail packaging. A householder buying diatomaceous earth is buying an unknown material that shares a name with an effective one.

14.3 The regulatory position elsewhere

The same paper notes that in Europe, the use of silicon dioxide is restricted to professionals, while diatomaceous earth can be harmful to the lungs.¹¹

That is an unusual arrangement worth noting: the more effective material is restricted, and the less effective one that carries the respiratory concern is freely available.

15. Resistance and persistence

The genuine advantages of the category deserve statement alongside the criticisms.

The mode of action limits the possibility of resistance developing because it is physical rather than chemical or metabolic, and diatomaceous earth is not even listed by the Insecticide Resistance Action Committee.⁸

Being silica based it has an extremely long shelf life, with one study finding a silica-based product still efficacious after 406 days of storage. It has an extremely long residual action and tends to be nullified only by the build-up of dirt, household dust and other debris. It leaves no chemical residue and has extremely low mammalian toxicity.⁸

15.1 The prophylactic argument

Because of the long residual action, there is strong potential for these dusts to be employed prophylactically.⁸

That is a real advantage over any liquid residual, which as the preceding article showed begins losing availability within the first hour on a porous surface.

15.2 The tolerance caveat

The resistance claim requires the qualification of §10. The mechanism does not select for resistance directly, but a population already carrying cuticular modifications from other selection pressure shows measurable tolerance.¹

15.3 An unexplained finding

One observation in the literature is left unresolved by its own authors. Ethanol was found to degrade efficacy substantially, and the authors remark that for an inert silica-based compound it seems strange that ethanol would degrade the efficacy to such an extent.⁸

We have no explanation either, and record it because it suggests the material is less inert in practice than its description implies.

16. The crystalline silica problem

The health question is specific and is not addressed by the word natural.

Some forms of diatomaceous earth contain crystalline silica. Filter grade or pool grade material is heat treated and contains a very high concentration of crystalline silica, up to 60 to 70 per cent.¹²

16.1 Against the pest management specification

Recall from §4.2 that material intended for pest management should contain less than 1 per cent crystalline silica.⁴

The gap between under 1 per cent and 60 to 70 per cent is the difference between two materials sold under the same common name, and a purchaser who buys pool filter grade because it is cheaper and more available has bought something categorically different.

16.2 The exposure route

The powder is extremely fine and can easily become airborne during normal activities.¹³ Diatomaceous earth can cause skin irritation and dryness, can irritate the nose and nasal passages during breathing, and in the case of inhalation of large amounts can contribute to coughing and shortness of breath.⁷

16.3 The conditions for serious harm

The published framing is careful and we reproduce it rather than overstating. Silicosis and related problems can potentially occur after chronic exposure, when the material contains high percentages of crystalline silica, and in workers mining diatomaceous earth and related materials.⁷

These are occupational conditions. A single careful crack and crevice application in a home is not the exposure scenario the silicosis literature describes, and it would be alarmist to suggest otherwise.

17. The occupational evidence

The underlying epidemiology is worth reporting because it establishes that the hazard is real rather than theoretical.

There is limited and conflicting evidence regarding the exposure-response relationship between exposure to crystalline silica and silicosis, and the level of risk to current workers remains uncertain. An epidemiological investigation of 1,809 workers in the diatomaceous earth industry, where exposures to crystalline silica are primarily to the cristobalite form, found that on the basis of the median of three independent readings, 81 workers, or 4.5 per cent, were judged to have opacities on chest radiographs. Age-adjusted relative risk of opacities increased significantly with cumulative exposure to crystalline silica.⁷

17.1 The wider literature

The same reference set includes extended follow-up of lung cancer and non-malignant respiratory disease mortality among California diatomaceous earth workers, and quantitative risk assessment of exposure to crystalline silica, silicosis and lung disease other than cancer in that industry.⁷

An additional finding of interest: a silicious dust that produces cell damage may be cleared more effectively from the lung than an innocuous dust, which is a counterintuitive result about pulmonary clearance.⁷

17.2 The proportionate conclusion

Mining and processing workers with years of daily exposure are not householders applying a dust to a bed frame. The relevance is that the material is not biologically inert, that the hazard scales with crystalline content and cumulative exposure, and that broadcast application in living space moves a householder along that axis rather than off it.

18. Application matters more than product

The regulatory guidance follows directly from §16 and §17 and is the single most useful practical statement in this area.

Pesticide dusts should be applied only in small cracks and crevices, rather than broadcast across floors or bedding where dust can easily become airborne.¹³

18.1 Why this is also better pest control

The guidance is usually presented as a safety measure, and it is, but it is also better technique.

A visible layer of dust across a floor is avoided by insects, disturbed by occupants, degraded by household debris as §15 notes, and airborne. A light deposit in the void where the insects actually harbour is contacted by the target and not by the occupant.

18.2 The broadcast failure mode

Broadcast application is what a householder does, because it is intuitive and because the product is cheap. It maximises the hazard and minimises the effect, which is a poor combination, and it is plausibly part of why field results differ from laboratory results.

We flag that last inference as ours. The double-blind and field studies cited here used defined application rates rather than consumer practice.

19. What this means for practice

Prefer silica gel where the choice exists. Three to four days against fourteen at label rate,¹ better performance at lower concentration against stored product pests,² and consistent superiority against resistant tropical bed bug strains.⁹

Apply at label rate. Tolerance in the resistant strain appeared at sub-label exposure.¹

Cracks and crevices only. Both for exposure and for efficacy.¹³

Do not expect knockdown. Death follows loss of about 60 per cent of water content² and these are slow acting by definition.⁶

Consider humidity. A mild desiccant is not effective when air is moist and has little evaporative power.⁶

Combine with activation where possible. Dust alone cleared none of six dormitories; dust with carbon dioxide cleared five of five.⁶

Treat source and grade as material. Supermarket diatomaceous earth was ineffective where professionally supplied material was not.¹¹

20. What this means for a Manitoba householder

A calibrated summary for the person most likely to encounter this product.

The dry winter interior favours the mechanism. This is a genuine local advantage and one of the few in this journal.⁶

The bag from the garden centre may be inert. Supermarket and litter-conditioner grades were found ineffective.¹¹

Never use pool or filter grade indoors. Up to 60 to 70 per cent crystalline silica¹² against a pest management specification of under 1 per cent.⁴

Do not spread it across floors or bedding. This is where both the hazard and the wasted product come from.¹³

Expect weeks, not days. Even effective material took nine to fifteen days against adults in laboratory conditions.¹

Natural is a description of origin, not of safety. That is the point of §16 and §17.

21. Limitations and open questions

The efficacy literature is genuinely contradictory. Laboratory work shows diatomaceous earth reaching 100 per cent mortality,¹⁸ while a field trial and a double-blind study show it largely ineffective.¹⁵ We have set out both rather than choosing.

We have not named commercial products in the comparisons. The studies name them; we have described them by active material, because we purchase these products and a ranking from us is not an appropriate source.

The occupational data concern industry workers. The 1,809-worker cohort is a mining and processing population, not applicators or householders.⁷

Sections 13.2 and 18.2 are our reasoning. The explanation that behavioural contact drives the laboratory and field gap, and that broadcast consumer application contributes to it, follow from cited findings but are not conclusions the authors drew.

The ethanol finding is unexplained. Reported in §15.3 because the original authors themselves flagged it as strange.⁸

No Canadian data. We have found no Canadian evaluation of desiccant dust performance, and given that interior relative humidity here varies more across the year than in most places studied, the humidity dependence makes this an unusually relevant gap.

We sell dust applications. This article argues the consumer version of the product is frequently ineffective and that the professional alternative is better, which is a conclusion that favours us and should be weighed accordingly.

22. Conclusion

Desiccant dusts kill by removing the epicuticular lipid layer through abrasion or sorption, after which the insect dies from evaporative water loss once it has lost roughly 60 per cent of its water content.²⁴ The mechanism was described in 1930,³ it is physical rather than metabolic, and the material remains active for months or years.⁸

The two forms are not equivalent. Silica gel produced complete mortality in three to four days where diatomaceous earth required fourteen,¹ it controls stored product pests at significantly lower concentration,² and it outperformed against resistant tropical bed bug strains.⁹ Since diatomaceous earth has two mechanisms and silica gel has one, the reasonable inference is that sorption does nearly all the work and the sandpaper story describes the lesser half.

Field performance is another matter. A double-blind evaluation found diatomaceous earth products delivering 11 per cent control or less,⁵ supermarket grade material was ineffective where professional grade was not,¹¹ and dust alone cleared none of six dormitories while dust combined with carbon dioxide release cleared all five.⁶ A passive deposit only works on an insect that walks through it.

And the natural framing does real harm here. Pest management grade material should contain under 1 per cent crystalline silica;⁴ filter grade can contain 60 to 70 per cent.¹² An investigation of 1,809 diatomaceous earth industry workers found radiographic opacities in 4.5 per cent with risk rising significantly with cumulative crystalline silica exposure.⁷ The guidance to apply dusts only in cracks and crevices rather than broadcast across floors and bedding¹³ is simultaneously the safety instruction and the efficacy instruction, which is a rare and convenient alignment and almost nobody follows it.

References

1. Lilly, D.G. et al. Evidence of Tolerance to Silica-Based Desiccant Dusts in a Pyrethroid-Resistant Strain of Cimex lectularius (Hemiptera: Cimicidae). PMC. Source for the evaluation of a silica gel and a diatomaceous earth product against pyrethroid-resistant and susceptible bed bug strains; label-rate doses producing 100 per cent mortality in both strains over three to four days with silica gel against fourteen days with diatomaceous earth; sub-label exposure indicating the resistant strain survived 50 per cent longer; the statement that diatomaceous earth is both abrasive and sorptive while silica gel is non-abrasive; the finding that against various stored product pests diatomaceous earth is significantly less effective than non-abrasive silica gels even at higher doses; laboratory efficacy at 1 to 8 grams per square metre achieving 100 per cent adult mortality over 9 to 15 days and 99 per cent nymph mortality after 2 days; and the acknowledgement of a field trial and a double-blind laboratory study presenting evidence that diatomaceous earth may be largely ineffective. https://pmc.ncbi.nlm.nih.gov/articles/PMC5198222/
2. Evaluation of diatomaceous earth formulations enhanced with natural products against stored product insects. Journal of Stored Products Research. Source for sorption of the wax layer and abrasion of the insect cuticle as the key parameters of activity citing Ebeling (1971) and Korunic et al. (2016); the finding that death occurs when the insect loses about 60 per cent of its water content, determining these as slow acting insecticides; and the observation that amorphous silica gel effectively controls insects at significantly lower concentration than diatomaceous earth while significantly reducing bulk density and flowability of grain. https://www.sciencedirect.com/science/article/pii/S0022474X19304928
3. Lipid adsorption of diatomaceous earths and increased water permeability in the epicuticle layer of the cowpea weevil and the bean weevil. Journal of Stored Products Research. Source for the finding that removal of epicuticular lipids by mechanical, chemical or high temperature treatment significantly increases cuticle permeability; the description of diatomaceous earth as an adsorptive dust containing fine amorphous silica particles; the dependence of efficacy on amorphous silica content with uniform particle size below 10 micrometres, high oil sorption capacity, large active surface area and very little clay or metal oxides; and the development of the mode of action of inert dusts as early as 1930 by Zacher and Kunike, attributing it mainly to desiccation. https://www.sciencedirect.com/science/article/abs/pii/S0022474X1530028X
4. Technology Spotlight: Diatomaceous Earth, and Bed Bug Supplement: Diatomaceous Earth, Where Do Bed Bugs Stand When the Dust Settles? Pest Control Technology. Trade publication reporting university research. Source for inert dusts killing by desiccation through removal of the outer wax layer rather than by absorbing water; the parameters affecting efficacy including particle size, shape, active surface area, oil absorption, pH, density, age and species of diatoms; the commercial oil absorption range of 116 to 175 per cent; the ideal specification of high purity amorphous silica below 10 micrometres with very little clay and less than 1 per cent crystalline silica citing Ebeling (1971) and Quarles and Winn (2006); the description of diatomaceous earth as fossilised diatoms acting like superfine sandpaper; silica gels as synthetically produced compounds of 99.5 per cent silicon dioxide functioning like a sponge; and the electrostatic charge of silica gel particles helping them adhere to insects. https://www.pctonline.com/article/pct1213-diatomaceous-earth-study/
5. Long-Term Efficacy of Various Natural or Green Insecticides against Bed Bugs: A Double-Blind Study. PMC. Source for the finding that a product containing 95 per cent diatomaceous earth with 0.25 per cent dinotefuran killed 27 per cent of bed bugs or less depending on strain and substrate; that a diatomaceous earth product and a botanical product produced 11 per cent control or less; that a silicate-based product showed no activity; the inclusion of a 100 per cent amorphous silica gel product applied at 2 ounces per 100 square feet; and the three-way interaction between treatment, substrate and bed bug strain. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4592613/
6. Non-hazardous pest control, patent background, together with dormitory field trial material reported in the diatomaceous earth health literature. Source for the description of dust media affecting insects slowly with gradual reduction in activity, slow weight loss and eventual death without rapid knockdown; diatomaceous earth as a mild abrasive and desiccant that abrades the cuticle and adsorbs the epicuticular wax layer; the observation that some but not all insects losing the wax layer under dry conditions succumb within hours; the protective basal cement layer in the cuticle affording additional desiccation protection; the statement that a mild desiccant is not effective when air is moist and has little evaporative power; and the dormitory result in which all five rooms treated with desiccant dust plus carbon dioxide were freed of bed bugs while none of six treated with dust alone were, attributed to longer activation and higher carbon dioxide dose in the field. https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/6713518
7. Harmful Effects of Bed Bug-Killing Method of Diatomaceous Earth on Human Health. Journal of Insect Science, 19(5), 13. Source for the epidemiological investigation of 1,809 diatomaceous earth industry workers with exposures primarily to the cristobalite form, finding 81 workers or 4.5 per cent judged to have opacities on chest radiographs and age-adjusted relative risk increasing significantly with cumulative crystalline silica exposure; the statement that evidence on the exposure-response relationship is limited and conflicting and risk to current workers remains uncertain; the observation that a silicious dust producing cell damage may be cleared more effectively from the lung than an innocuous dust; skin irritation, nasal irritation, coughing and shortness of breath from inhalation; and the three conditions under which silicosis and related problems can potentially occur, namely chronic exposure, high crystalline silica content, and workers mining these materials. https://academic.oup.com/jinsectscience/article/19/5/13/5586712
8. The Efficacy of Diatomaceous Earth against the Common Bed Bug, Cimex lectularius. Source for the dose series giving cumulative percentage mortality at 8, 4, 2 and 1 grams per square metre across nine days with all treatments statistically different from controls; the extremely long shelf life with a silica-based product still efficacious after 406 days of storage citing Tarshis (1962); the extremely long residual action nullified only by build-up of dirt, household dust and debris; the physical rather than chemical or metabolic mode of action limiting resistance development and the absence of diatomaceous earth from the Insecticide Resistance Action Committee listing; the absence of chemical residue and extremely low mammalian toxicity; the potential for prophylactic use; and the unexplained observation that ethanol degraded efficacy substantially. https://www.researchgate.net/publication/322974799_The_Efficacy_of_Diatomaceous_Earth_against_the_Common_Bed_Bug_Cimex_lectularius
9. Comparative evaluation of desiccant and chemical dusts against pyrethroid-resistant Cimex hemipterus. Source for the evaluation of two desiccant dusts and two chemical dusts against three pyrethroid-resistant C. hemipterus strains with documented cuticle variation compared with a susceptible C. lectularius strain, across continuous exposure, brief five-minute contact, sub-label application at 50 per cent rate and horizontal transfer; the finding that desiccant dusts and particularly the silica gel consistently achieved rapid and complete mortality in resistant strains, outperforming diatomaceous earth and pyrethroid-based dusts; and that a deltamethrin dust was largely ineffective while a pyrethrin, piperonyl butoxide and silica gel combination killed the susceptible strain. https://www.researchgate.net/publication/382557922_Bed_bug_control_with_various_dusts_Efficacy_comparison_between_silicon_dioxide_diatomaceous_earth_and_Sommieres_earth
10. Diatomaceous Earth, A Natural Insecticide for Stored Grain Protection: Recent Progress and Perspectives. Source for the composition of diatomaceous earth as amorphous hydrated silica from fossilised diatoms; the insecticidal action relying on cuticle abrasion combined with adsorption of protective lipids leading to progressive desiccation citing Ebeling (1971); the statement that toxicity arises primarily from physical attributes rather than chemical composition; the mechanisms of cuticular wax absorption, cuticle abrasion, digestive tract damage, surface enlargement through dehydration and obstruction of spiracles and tracheae; and the observation that cuticular damage may increase vulnerability to entomopathogenic infection. https://www.researchgate.net/publication/322194284_CHAPTER_10_Diatomaceous_Earth_A_Natural_Insecticide_for_Stored_Grain_Protection_Recent_Progress_and_Perspectives
11. Bed bug control with various dusts: efficacy comparison between silicon dioxide, diatomaceous earth, and Sommieres earth. Parasite. Source for the comparison of silicon dioxide and diatomaceous earth from a pest management company against diatomaceous earth sold as a litter conditioner, supermarket diatomaceous earth, green clay, talc and sodium bicarbonate across permanent exposure, short exposure, horizontal transfer and repellent effect on two bed bug colonies; the finding that Sommieres earth demonstrated efficacy from 75 to 100 per cent similar to professionally supplied diatomaceous earth while litter conditioner and supermarket diatomaceous earth, green clay, talc and sodium bicarbonate were ineffective; and the note that in Europe silicon dioxide use is restricted to professionals while diatomaceous earth can be harmful to the lungs. https://www.parasite-journal.org/articles/parasite/full_html/2024/01/parasite230173/parasite230173.html
12. Comparative consumer guidance on silica gel and diatomaceous earth products. Commercial source. Used only for the statement that filter grade or pool grade diatomaceous earth is heat treated and contains a very high concentration of crystalline silica, up to 60 to 70 per cent. Note the commercial interest in favouring one product category over another. https://pestzero.blog/cimexa-vs-diatomaceous-earth/
13. Guidance on diatomaceous earth use and inhalation risk, citing United States Environmental Protection Agency, National Pesticide Information Center, Centers for Disease Control and Prevention and National Institute for Occupational Safety and Health materials. Source for the recommendation that pesticide dusts be applied only in small cracks and crevices rather than broadcast across floors or bedding where dust can easily become airborne; the report that inhaling diatomaceous earth dust can irritate the nose and lungs and may cause coughing or breathing discomfort; the warning that inhaling respirable silica particles can damage lung tissue and contribute to diseases such as silicosis; and the caution that marine or saltwater diatomaceous earth contains much higher crystalline silica concentrations and should never be used indoors. https://convectex.com/blogs/blog/will-diatomaceous-earth-kill-bed-bugs-why-it-often-fails